1. Field of the Invention
The present invention relates to a screen-input image display device, and more particularly to a screen-input image display device incorporating a capacitive touch panel in an image display panel.
2. Description of the Related Art
There are screen-input image display devices which are equipped with a touch sensor (also referred to as a touch panel) that has the function of inputting data (screen-input function) when a user touches (touches or presses, referred to below simply as touching) a display screen such as a liquid crystal display panel with a finger or the like. Screen-input image display devices are used in mobile electronic devices such as PDA or portable terminals, various types of household electrical devices, and stationary customer guidance terminals such as unmanned receptionist machines. Known examples of such touch-input implementation systems include systems for sensing changes in the resistance or changes in the capacitance of parts that are touched, and systems for sensing changes in the luminous energy in parts that are blocked by touch.
FIG. 14 is a schematic view illustrating the structure of a touch panel used in a system for sensing changes in resistance. FIG. 15 is a conceptual view illustrating a method for sensing touch locations on the touch panel illustrated in FIG. 14. In the touch panel in FIG. 14, a solid transparent conductor film 2 is formed on one side of a substrate on the side where the display device is viewed, and electrode terminals 4 (4A, 4B, 4C, 4D) are provided in the four corners. As shown in FIG. 15, an alternating current signal AC is applied to the transparent conductor film 2 for sensing coordinates; current i1, i2, i3, and i4 flowing to current sensing resistors r1, r2, r3, and r4 located in the four corners is sensed; and the coordinates are calculated from the proportion of electrical resistance between the locations touched by the finger and the electrode terminals 4.
FIG. 16 is a conceptual view illustrating the structure of a touch panel used in a system for sensing changes in capacitance. In this touch panel, sensor cells X1, X2, and X3 in a direction X and sensor cells Y1, Y2, Y3, Y4, and Y5 in a direction Y are arranged on a transparent substrate; and each of the sensor cells in the Y direction is electrically connected by electrical wire connections 38, 40, and 41 which have been made outside the sensing areas. Coordinates which have been touched are sensed through the calculation of the level of current picked up by the X-direction sensor cells (electrode pads) X1, X2, and X3 and the Y-direction sensor cells Y1, Y2, Y3, Y4, and Y5.
Because touch panels in systems for sensing changes in capacitance can be formed with just a single transparent conductor film, the structure is simple, and a characteristic feature of systems for sensing changes in capacitance is that, unlike systems for sensing changes in resistance, input coordinates can be sensed without applying pressure to the display panel side.
JP-A 2003-66417 and 2007-18515 are examples disclosing a screen-input image display device in which changes in capacitance are sensed. JP-A 2003-66417 discloses a capacitive touch panel in which a location-sensing transparent conductive film is provided to the opposite side of a glass substrate equipped with counter electrodes for a liquid crystal display panel, and oscillating voltage is applied to the transparent conductor film, whereby current flowing to the touching finger is sensed, and the coordinates are sensed. JP-A 2007-18515 discloses a capacitor sensor equipped with a substrate, on one surface of which are arranged electrodes that comprise a transparent conductor film or the like, the electrodes being arranged in such a way as to define arrays of sensor cells arranged in rows and columns for forming sensing areas.